峨眉山玄武岩和白马层状岩体的铬镍地球化学

文章讨论了峨眉山玄武岩及白马基性、超基性岩体的微量元素地球化学特征。对Cr、Ni富集的地球化学条件进行了探讨,认为在母岩浆分离结晶早期形成的堆积层,即结晶度很小的橄榄岩有利于寻找富Cr、Ni层位。

Chromium And Nickel Geochemistry Of Emei'shan Basalt And Baima Layered Intrusion

Trace element geochemical characteristics of Emeishan basalt and Baima basic and ultrabasic intrusive body are discussed in this paper. The crystallinity of Emeishan basaltic magma might be determined by Th content of the rock formed by the original Emeishan basaltic magma and that of basalt produced by the residual magma. Nevertheless, as Baima basic and ultrabasic layered cumulate was formed by cumulus of basaltic magma, the crystallinity of magma during the formation of the layered cumulate should be determined by means of crystallinity of nickel at its transition point. Geochemical environments of the Cr- and Ni-rich accumulated bed are studied, a tentative discussion is given on the relationship between chromium and nickel in basalt and layered cumulate respectively. From the equation for element abundance relationship of rocks formed at the same crystallization stage of the same magma, the equations for relationship of chromium and nickel abundances in peridotite (cumulate) and basalt are derived and, on such a basis, the partition coefficients of chromium and nickel at the early stage of magmatic differentiation and crystallization can be evaluated. From the relationship between chromium and nickel abundances in cumulus and the geochemical environment of Cr-rich accumulated bed, it is known that the crystallization and accumulation period of peridotite iron ore was too late for the enrichment of nickel and, especially, chromium, and that one should seek for earlier products of magmatic differentiation and crystallization in search for chromium and nickel deposits and accumulated beds enriched in cbromium and nickel. Previous researches demonstrated that the vanadic titanomagnetite ore and its wall rocks in Baima cumulate were formed respectively by Fe-rich ore magma and silicate magma generated as a result of liquation at the early evolution stage of the original basaltic magma. Further investigation into the conditions for chromium and nickel enrichment requires more knowledge on geochemical behaviors of chromium, nickel and iron in the process of the liquation of ore magma.